The present invention relates to digital data communication and more particularly to a system and method for data synchronization in digital data communication.
Data synchronization is a well known process in the art of digital communication, serving to ensure that a receiver will sample each data symbol of the received signal at one or more points in time during the presence of the data symbol at which the data symbol is stable. A typical approach is to sample the data symbols as close as possible to their center.
In a short-range wired communication system, the transmitting device typically sends a data signal and a separate clock signal. The clock signal indicates to the receiving device when to sample the data. In SDR systems, where each bit of data is accompanied by a pulse of the clock, there is generally no need for the receiving device to adjust the timing of the sampling of the data, and no special synchronization process is required.
However, in modern data communication devices, the bit rate of the data is often higher than the pulse rate of the clock, as is the case, for example, in DDR (Double Data Rate) and QDR (Quad Data Rate), which are two approaches to transmission of data at bit rates greater than the clock rate. In such systems, the receiver has to create a sampling signal that has a frequency higher than the clock frequency, typically an integer multiple of the clock frequency, and sample the bit stream using this frequency-multiplied sampling signal.
In DDR and QDR systems that support bi-directional communication between two devices, one approach is for each of the devices to have its own clock. Typically, the clock of the transmitting device act as the primary frequency standard, and the receiving device synchronizes on the clock of the transmitting device. This half-duplex method is known in the art as “source synchronous”.
When the direction of transmission is reversed the clock of the formerly receiving, and now transmitting, device becomes the primary frequency standard, and the clock of the formerly transmitting, and now receiving, device synchronizes on the clock of the transmitting device.
With the development of electronic devices, such as data storage devices, it has become possible to make portable devices very small. With miniaturization, however, power consumption and connectivity are more challenging.